An increasingly popular process for forming composites is by compression molding or stamping a moldable sheet of a thermoplastic resin reinforced with fibers such as a glass fiber mat, often referred to as glass mat thermoplastics or "GMT". These composite sheets can be used to form articles such as automobile components and housings for computers.
An example of a commercially successful GMT sheet is the AZDEL.RTM. moldable composite sheet which is formed by extruding layers of polypropylene resin sheet with needled mats of continuous glass fiber strand. The AZDEL.RTM. composite sheet is commercially available from Azdel, Inc. of Shelby, N.C.
For reinforcing a resin matrix material, U.S. Pat. Nos. 3,664,909, 3,713,962 and 3,850,723 disclose fibrous mats of unstranded filaments which can be layered with reinforcing mats of fiber strands.
U.S. Pat. No. 4,847,140 discloses an insulation medium formed by needling a loose layer of inorganic fibers, such as glass, bonded together by a carrier web which is a blend of inorganic and organic fibers, with the carrier web comprising up to about 10% by weight organic fibers.
U.S. Pat. Nos. 4,948,661, 5,011,737, 5,071,608 and 5,098,624 disclose fiber reinforced thermoplastic molded products produced by intimately blending reinforcing glass fibers and thermoplastic fibers into a web and heating the web to the melting point of the thermoplastic fibers while applying pressure to the web to press the web into a consolidated structure.
There is a long-felt need in the industry for a mat for applications such as GMT which can be readily handled, processed and impregnated by the thermoplastic matrix material, good uniformity of glass distribution and flow into complex mold shapes, low composite viscosity and which provides a composite having good surface smoothness and mechanical properties, such as strength and stiffness.